Conventional motor vehicles using diesel as fuel are generally equipped with an electronically regulated common rail injection system. These motor vehicles are subject to legislation for exhaust gases which, especially in large areas of the USA and other countries having comparable CARB (California Air Resources Board) legislation, require system-immanent monitoring of emissions of the motor vehicle. Violations of emissions limits by, for example, incorrect quantities in the fuel injection system must be diagnosed in the shortest possible periods of time and be displayed by activating an indicator lamp.
This requirement is fulfilled by monitoring an adaptation value of a speed-based zero quantity calibration, whose actual purpose is the adaptation and compensation of fuel-quantity drift of an injector over its lifetime. In a zero quantity calibration, the quantity of the fuel to be injected is increased in small steps until a noticeable change in speed of the motor vehicle's internal combustion engine is present. If the adaptation value is outside of a required interval, the injector is diagnosed as defective. A disadvantage of this method, primarily from the point of view of a customer, is a logistically complex and time-consuming application of the underlying zero quantity calibration, which is specific with regard to the drive train and vehicle.
From a technical perspective, a comparable method for monitoring the adaptation value of a drive train-independent zero quantity calibration is likewise implementable in order to identify a defective injector, making it possible to eliminate the above-named disadvantages of an application specific to a drive train. In a drive train-independent zero quantity calibration, a drive train of the motor vehicle is simulated by a model. However, such a method will not be able to satisfy the stringent requirements of the CARB legislation with respect to speed of diagnosis, since the drive train-independent zero quantity calibration has a significantly lower adaptation speed than the drive train-dependent zero quantity calibration due to its functional principle.